A heating system is designed to keep the inner wall surfacetemperature of a room at
25ï‚°C. Only one wall of the room is contacted with the outerenvironment. The crosssectional view of the wall is schematicallyshown in Fig. H1. The height, width and
thickness of the wall are 2.5 m, 10 m and 0.2 m, respectively.The wall is made from red
bricks with a thermal conductivity of 0.72 W/m.K and solarabsorptivity of ï¡s = 0.63.
The temperature and velocity of the ambient air stream are 1ï‚°Cand 20 km/h,
respectively at the outside. In addition, solar irradiationcoming to the wall surface is
40 W/m2. Considering the given “day†conditions of winter,
a. Make an energy balance on the outer surface of the wall (showall input and output
streams). [3pts]
b. What is the outer surface temperature of the wall?[10pts]
c. What is the total heat loss from the wall? [2pts]
d. If an insulating material with a thickness of 3 cm and athermal conductivity of
0.05 W/m.K is mounted to the adjacent of the wall (from roomside), how is the outer
surface temperature and heat loss from the wall changed? Whateffect would such
an application have? [5pts]
e. How is the total heat loss from the wall with no insulationchanged if the wind speed
increases to Uï‚¥= 40 km/h at the outside environment. Determinethe percentage
increase/decrease in the heat loss, when compared to heat lossfound in (c.). [5pts]
